Date Code 20020129
Differential, Restricted Earth Fault,
3-63
Overcurrent, Voltage, and Frequency Elements
SEL-387E Instruction Manual
Setting Descriptions
Recommendations
Collect this information before calculating volts/hertz element settings:
Transformer manufacturer’s overexcitation limit curve
Transformer nominal phase-phase voltage
Select the transformer winding that is most likely to suffer overexcitation. The relay voltage
input should be from a source that most reliably reflects that winding voltage.
Use the Level 1 volts/hertz element as an overexcitation alarm. Set 24D1P equal to or greater
than 105 percent, but less than the minimum pickup of the Level 2 element. Use a 24D1D time
delay of 1.0 second to allow time for correction of an overexcitation condition prior to an alarm.
Use the Level 2 volts/hertz element as an overexcitation tripping element. Select the dual level,
composite inverse, simple inverse, or user-defined operating time characteristic (using the
SEL-5806 Curve Designer Software) to conform to the transformer manufacturer’s
recommendations.
Phase Potential Connection (DELTA_Y)
Use
SET G <ENTER>
to access the DELTA_Y setting. Set DELTA_Y = D for open-delta PT
connections (Figure 2.16), otherwise, set it to Y. See
Phase Potential Connection (DELTA_Y)
in
Section 6: Setting the Relay
for more information on this type of PT connection.
Volts/Hertz Protection Enable (E24)
Range
: (Y,
N)
Set E24 = Y to enable volts/hertz protection elements. If you do not need volts/hertz protection,
set E24 = N. When E24 = N, the 24TC, 24D1, 24D1T, 24C2, 24C2T, and 24CR Relay Word bits
are inactive. The relay hides corresponding settings; you do not need to enter these settings.
Protected Winding Line-to-Line Voltage (VNOM)
Range
: (0.20
– 800.00 kV)
VNOM is the rated transformer line-to-line voltage in kV at the protected winding. Consider the
transformer tap when determining this setting. For example, a 345 kV transformer set on the
327.75 kV TAP would have VNOM = 327.75.
Power Transformer Winding Connection (24WDG)
Range
: (D,
Y)
When three PTs are available, the most common PT winding connection is to connect both HV
and LV sides in wye, leaving the power transformer winding connections as the only variable.
For wye-connected power transformer windings, the power transformer phase-to-neutral voltage
is readily measured through wye-wye connected PTs. Set 24WDG = Y. When the power
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